Xylitol is one of the few household substances where a small quantity produces a rapid and serious effect in dogs. The mechanism is a species difference in how the body reads it.
The species difference at the centre of it
Xylitol is a sugar alcohol used as a sweetener, and in humans it is absorbed slowly and provokes little insulin response.
In dogs the pancreas responds to it as though it were glucose, releasing insulin in proportion to a sugar load that is not actually present.
Insulin then moves genuine glucose out of the bloodstream, and blood sugar falls sharply because nothing arrives to replace it.
How quickly it happens
The drop can begin within a short period of ingestion, and it develops considerably faster than most household poisonings.
Signs reflect the brain being deprived of glucose: weakness, unsteadiness, disorientation, collapse and in severe cases seizures.
Some products delay absorption, so a normal-looking dog in the first hour does not mean the exposure was inconsequential.
The second, separate effect
At higher exposures a distinct problem appears, involving damage to the liver that is not explained by the blood sugar drop.
This can develop over a longer period, in some cases after the initial episode has apparently been managed.
Because the two effects have different thresholds and timelines, a dog may need monitoring well beyond the point at which it appears recovered.
Where it turns up
Sugar-free chewing gum and mints are the classic sources, and gum is particularly significant because the amount per piece varies widely between products.
It also appears in sugar-free baked goods, some peanut butters, protein bars, certain toothpastes and mouthwashes, and a number of liquid medications and supplements.
Peanut butter is the source most likely to catch owners out, because it is routinely used to fill toys and administer tablets, and few people check the label for a sweetener.
Why household checking matters more than caution at the moment
The quantities involved are small enough that ordinary vigilance around food does not reliably prevent exposure.
Reading labels on anything sugar-free that comes into the house, and keeping bags and coat pockets out of reach, addresses the realistic route.
Any suspected ingestion is an immediate veterinary call rather than a wait-and-see situation, with the packaging available so the quantity can be assessed.